1. Field of the Invention
The present invention relates to a plasma processing apparatus for supplying processing gas into a processing chamber arranged within a vacuum reactor and generating plasma so as to process wafers placed in the processing chamber, and after ending the process, supplying inert gas into the processing chamber and then opening the vacuum reactor to atmosphere.
2. Description of the Related Art
Plasma processing apparatuses such as semiconductor wafer processing apparatuses supply processing gas into a processing reactor depressurized to vacuum state (hereinafter referred to as a vacuum reactor) and forming plasma. Therefore, in order to perform maintenance of the interior of the vacuum reactor, it is necessary to return the interior of the vacuum reactor to atmospheric pressure before opening the reactor for maintenance.
One method for returning the pressure within the vacuum reactor to atmospheric pressure is to supply inert gas into the vacuum reactor and purging the interior thereof. Purging is a process of displacing the atmosphere within the reactor and pipes with inert gas, and for example, inert gas is supplied into an airtightly sealed reactor maintained in vacuum so as to displace the interior of the reactor with inert gas, to thereby raise the pressure within the reactor and to enable the reactor to be opened to the atmosphere. Furthermore, if hazardous gases or reactive gases exist in the reactor, the supply of inert gas into the reactor enables the atmosphere within the reactor to be displaced with inert gas, so that the hazardous gases and reactive gases in the reactor can be eliminated (removed) from the reactor.
Japanese patent application laid-open publication No. 2005-216982 (patent document 1) discloses such prior art method, wherein an inert gas supply pipe is connected between a processing gas supply source and a mass flow controller (MFC) for controlling the flow rate of the processing gas, so as to purge the MFC, the processing gas supply pipe and the interior of the processing chamber. Especially, the invention disclosed in patent document 1 is equipped with a sensor for detecting the processing gas concentration, aimed at achieving the object of determining the end of the purging operation by detecting the gas concentration within the processing chamber.
However, the aforementioned prior art plasma processing apparatus and the method for purging the same had the following drawbacks. Plasma processing apparatuses are equipped with a member having a plurality of small holes formed thereto (hereinafter referred to as shower plate) disposed between the processing chamber and the processing gas supply pipe for feeding the processing gas supplied from the processing gas supply source via the processing gas supply pipe uniformly in a dispersed manner into the processing chamber. The shower plate is formed of a dielectric member such as quartz for transmitting the electromagnetic waves radiated via the antenna from a high frequency power supply into the processing chamber. The processing chamber is separated into two chambers, a processing chamber and a thin clearance above the shower plate (on the gas supply side) via the shower plate.
Upon performing maintenance, when a purging operation using inert gas is performed through the processing gas supply pipe, since the conductance of the large number of holes on the shower plate is small, an excessive pressure difference occurs between the pressure in the thin clearance above the shower plate and the pressure in the processing chamber, by which the shower plate formed of a fragile material may be damaged.
In order to prevent damage of the shower plate, a method is adopted in which the inert gas is supplied through a side wall of the vacuum reactor and not through the processing gas supply pipe, but according to this method, the purging of the interior of the processing chamber can be performed sufficiently, and as mentioned earlier, since the diameter of the large number of holes on the shower plate is small and the conductance thereof is small, not enough inert gas will reach the thin clearance above the shower plate separated by the shower plate from the processing chamber or the processing gas supply path including the processing gas supply pipe, so that the purging operation becomes insufficient, and processing gas may reside in the processing gas supply path.
Moreover, since the purging of the processing gas supply path is insufficient, the processing gas supply path is at a state where the pressure is lower than atmospheric pressure or at negative pressure when the chamber is opened to the atmosphere, so that the processing gas supply path will suck in atmosphere when opened to the atmosphere, and the residual processing gas within the processing gas supply path and the moisture in the atmosphere will cause the corrosion of the processing gas supply path.